This invention is concerned with positive displacement pumps and is concerned with pumps of the general kind described in U.S. Pat. No. 3,168,872, issued Feb. 9, 1965 to Pinkerton. The basic pump of that patent comprises a cylinder, a piston forming, with the cylinder, a working chamber and mounted for rotation and reciprocating sliding movement in the cylinder. A drive effective to provide that rotary and reciprocatory movement is provided, that drive being connected to a piston rod secured to the piston. Inlet and outlet ports are provided for the admission and exit of fluid from the cylinder and the piston has a duct which sequentially provides communication between the inlet port and the working chamber and between the outlet port and the working chamber.
The aforementioned patent illustrates a double monoplex version of the pump and a duplex version of the pump besides the single monoplex version described hereabove. In each of the double monoplex and duplex pumps the piston has ducts at each end and divides the cylinder into two working chambers, one at each end of the piston. In the double monoplex pump, each chamber has an inlet and an outlet port and the arrangement is such that as one chamber expands during reciprocal movement of the piston, the duct at the corresponding end of the piston registers with the inlet port to that chamber while the other chamber reduces in volume and the other duct registers with the outlet port from that other chamber. In this way there is achieved the pumping action of two single pumps, i.e. there is achieved a double monoplex action.
The duplex pump of the aforementioned patent has a single inlet port and a single outlet port and the arrangement is such that the ducts connect the chamber of the cylinder which is expanding with the inlet port and the chamber of which the volume is being reduced with the outlet port.
The point to be made concerning the double monoplex and duplex pump described in the patent is that the patentee failed to ascribe any significance to the fact that the presence of the piston rod is one of the chambers is effective to make the volume swept by the piston in that chamber lesser than that swept by the piston in the other of those chambers so that the volumes of the two working chambers is appreciably different. The shortcomings resulting from this characteristic are apparent.
The failure to attribute significance to this characteristic or even to recognize it is not an aberration to which only the inventor of the pump of the aforementioned patent is subject. Reference is made to the disclosure of Arp's U.S. Pat. Nos. 3,530,872 and 3,530,873 and to Malburg's U.S. Pat. No. 2,203,832, each of which illustrates a double acting piston/cylinder type pump of which the difference in volumes of the working chambers at each side of the piston is present but in each one of which the failure to recognize this characteristic has introduced a distinct error.
In Arp, U.S. Pat. No. 3,530,872, there is shown a double acting piston/cylinder unit for handling oxygen in a respirator system and the piston of that unit is ganged to a single acting piston cylinder for handling the air or other fluid to be mixed with the oxygen. Referring specifically to FIG. 2 of that patent, it will be apparent that the quantity of oxygen moved from one side to the other of the double acting piston as that piston moves from right to left will be in excess of that which can be accommodated on the other side of the piston and, as a result, that excess oxygen must pass to the outlet and, of course, will not be mixed with the second fluid.
In Arp's U.S. Pat. No. 3,530,873 a pair of double acting piston/cylinder units are illustrated, one of which meters the oxygen supply and the other of which meters the supply of another gas, such as air, the pistons of the two units being ganged by a common piston rod. Referring to FIG. 3 of the drawings of that patent, it is clear that the volume of oxygen delivered to the outlet line is greater in left to right movement of the piston than it is in right to left movement where exactly the opposite is true of the second fluid. As such, considerable errors are introduced in the proportions of the fluids in the mixture produced by that system.
In Malburg's U.S. Pat. No. 2,203,832, there is illustrated a system which purports accurately to proportion and mix two liquids, one of which two liquids, one of which is water and the other of which is embalming fluid. Since Malburg is concerned with a treatment of cadavers, the strictest accuracy is probably not necessary, nonetheless, this is the stated aim of the patentee and it is clear from a consideration of FIG. 1 of Malburg's patent that substantial error must occur in the proportions of the two fluids mixed. Considering that figure, it is to be observed that the amount of embalming fluid to be mixed with water during right to left movement of the pistons will exceed that amount delivered to be so mixed on left to right movement of the pistons. Since there is a by-pass between opposite sides of the piston/cylinder from which the embalming fluid is being delivered and since an additional mixing piston/cylinder device is provided, this error may be lessened to acceptable limits considering that the resulting mixture is utilized only on cadavers. Nonetheless, the error is present and it is clear that its presence was not recognized by Malburg.
According to one aspect of the present invention, double monoplex and duplex pumps of the kind generally described in Pinkerton's U.S. Pat. No. 3,168,872 are provided with means for equalizing the volume swept by the piston in the two chambers of the cylinder in such pumps. According to another aspect of the present invention, utilization is made of the characteristic of having different volumes of the chambers at each side of the piston to achieve proportional mixing, joining or separating of fluids handled by the pump.